1. Field of the Invention
The present invention relates to a disk device and a positioning control circuit for controlling the positioning of a head by suppressing the position shift caused by external vibration, and information processing apparatus using them, and more particularly to a disk device and a positioning control circuit for suppressing the vibration of a head caused by disturbance from the start of positioning control, and an information processing apparatus using them.
2. Description of the Related Art
For disk devices, such as magnetic disk device and optical disk devices, accurately positioning the head on the target track is extremely important to improve recording density.
Recently the application fields of disk devices are widening, not only for computers but also for portable electronic equipment and car navigation devices, etc. This spread of the application range means that disk devices receive various disturbances unlike prior art.
Generally the resonance frequency of a disk device is measured and the resonance frequency component is suppressed using a filter. Performing disturbance suppression control by learning disturbance using adaptive control has also been proposed (e.g. Japanese Patent Application Laid-Open No. 2000-21104).
Such disturbance countermeasures are based on the assumption that disturbance is unknown. Or it is assumed that disturbance is known and the frequency thereof does not change. For example, in adaptive control to follow up to the periodic disturbance, the initial frequency at which adaptive control operates is arbitrary, such as a value at the center of the frequency range where follow up is possible.
However as the application fields of disk devices spread, it is demanded to support not only the case of unknown disturbance frequency, but also the case when the disturbance frequency is known but changes, or the case when the disturbance frequency received by the disk device is unknown but is specific.
For example, mechanical resonance is generated between a disk device and the casing in which the disk device is installed. The disk device is supported on the casing by screws, rubbers or elastic materials. Therefore vibration is generated from the excitation source which is the reactive force to seek operation of the disk device. This frequency can be estimated in advance but changes depending on the type of the casing in which the disk device is installed.
Another example is vibration of another machine installed in the device where the disk device is installed. Specific examples are a vibrator of the portable telephone and the optical drive of a notebook personal computer and desk top personal computer. The vibrator generates vibration at a predetermined frequency. In an optical drive, vibration synchronizing with the rotation of the disk is generated according to the eccentricity of the disk to be mounted. These vibration frequencies are in many cases predetermined, or can be estimated. However the other equipments are not always operating, so the disturbance frequency is known but is not constant after all.
In conventional control against disturbance, it takes time to handle a disturbance of which frequency is known but not constant or disturbance of which frequency is unknown but specific not at random, and it is difficult to perform disturbance control, particularly against external vibration, immediately. For example, in the case of the above mentioned adaptive control to follow up the periodic disturbance, the initial frequency at which the adaptive control operates is set to a center value of the frequency range where follow up is possible, so it takes time to adapt to such disturbance frequency by learning.
Also as track density increases in the current situation, if the adaptation of such disturbance frequency delays, read errors and write errors frequently occur. These cause a drop in the read/write characteristics.